This invention relates to broadband cable service and more particularly, to an arrangement for detecting tampering with the broadband cable.
Modern broadband cable networks can provide broadcast video, video on demand, pay per view, primary line telephony, and high speed wide band data access all over the same physical medium that can be shared between 50 to 500 households. With the advent of primary line telephone service over these networks, network access is provided or prohibited using a network interface unit (NIU) normally located at the entrance to the customer""s premise. This entrance is normally on the back of the residence. The NIU is a network element that is owned and controlled by the service provider and not the consumer. The NIU establishes a clear point of demarcation between the customer premise and the cable network. It is to the service provider""s advantage to use a common NIU to control access to video, telephone, and high speed Internet data service. Hence, access to any particular service is either permitted or restricted using the electronics within the NIU. Therefore, theft of service or privacy violations require that this unit be bypassed and/or replaced by a modified unit. The NIU also assures that the privacy of an individual residence is protected from other residences. Within the prior art, it is known for service providers to perform periodic inspections to determine if an NIU has been bypassed or bridged so as to illegally receive broadcast video service or monitors another user""s Internet data. This practice is costly to perform and not particularly effective.
The problem remains to provide an effective and economic method for detecting if an NIU has been bypassed or bridged.
The foregoing problem is solved and a technical advance is achieved by detecting tampering of an incoming cable to which an NIU is connected by testing for a reflected signal that is present when the signal being transmitted to the head end is not connected to a properly terminated coaxial cable. In particular, by comparing the phase of the transmitted signal from the NIU with that of the reflected signal, a distinction can be made between a signal that travels many feet before being reflected back and a signal that reflects back right or near the connector of the NIU. Only the latter is used as a stimulus to indicate tampering since the first is likely caused by cable personnel disconnecting the cable further into the network. The key difference between the two types of reflected signals is the time delay of the reflect signal with respect to the transmitted signal from the NIU. Advantageously, the method can be used to detect a bridge tap, because the tap causes the characteristic impedance of the cable to decrease causing an infeed mismatch and subsequent reflected energy.
Advantageously, when tampering or a bridge condition is detected, the NIU disrupts service by disabling the video signal to the residence, disable Internet access, and disable telephony service with the exception of 911 calls and calls to the service provider. To restore service, the cable service provider intervenes and sends a specific data sequence to the NIU in order to restore service. The cable service provider then can investigate and determine the reason for the disruption.